This proposal will test the hypothesis that young children are an important source of CMV infection for their mothers and that maternal infection acquired from a child by a pregnant women can result in fetal infection. Our extensive work in CMV epidemiology, particularly recent studies of transmission of CMV among children and to their parents, coupled with knowledge that virtually nothing is known about sources of maternal CMV infection , led to formulation of this hypothesis and our plan for addressing it. Recognizing existing epidemiologic data that supports a role for sexual transmission, we also plan to evaluate the potential importance of this mechanism of maternal and fetal infection through a study of mothers of children with congenital CMV infection, utilizing a case-control design, and through longitudinal study of sexually active adolescents.